Energy, in the form of ATP, is produced in the lens primarily through glycolysis in metabolically active cells in the anterior lens. This process is required because the oxygen tension in the lens is much lower than that in other tissues, given that oxygen reaches the avascular lens only via diffusion from the aqueous humor.
Most of the glucose entering the lens is phosphorylated to glucose-6-phosphate by hexokinase, the rate-limiting enzyme of the glycolytic pathway. Under normal conditions, most glucose-6-phosphate passes through glycolysis, wherein 2 molecules of ATP are formed per original molecule of glucose. A small proportion of glucose-6-phosphate is metabolized through the pentose phosphate pathway (also called hexose monophosphate shunt). This pathway is activated under conditions of oxidative stress because it is responsible for replenishing the supply of nicotinamide adenine dinucleotide phosphate (NADPH) that becomes oxidized through the increased activity of glutathione reductase under such conditions (Fig 10-5).
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.